Various apparatus and methods have previously been devised to provide indication of the positioning of valve closing mechanisms. U.S. Pat. No. 3,701,362 to Reese, for example, describes a butterfly valve having a position indicator attached via a nose piece fitted into a transverse slot on the end of the valve drive shaft. The drive shaft is then attached by a pin to the vane of a butterfly valve. According to the patent, as the drive shaft is rotated to control the opening of the butterfly valve, the disclosed position indicator moves with respect to an exterior wall face of the butterfly valve. Another valve opening indicator system is described in U.S. Pat. No. 4,02,890 to Yasuoka. The disclosed apparatus here includes a scale plate attached to the valve case of a rotary valve by a projection. Attached to the valve stem below the valve handle is an indicating rod. Together the indicating rod and scale plate are supposed to constitute a way for determining the amount the valve is open. Still another valve position indicator system is described in U.S. Pat. No. 2,515,837 to Quinn. The indicator system disclosed in this patent is formed by an arcuately movable pointer and a pair of indicator-label plates attached to a valve mounted in a box. The arcuately movable pointer is provided on a plate attached to the valve spindle. The indicator-label plates are attached to an internal surface of the wall of the valve casing.
The above prior art valve opening indicator systems in many cases are complex requiring specially machined parts such as nose pieces with slots and pairs of indicator-label plates. Because of such mechanical complexity their assembly must be both time consuming and costly to implement. Also, such indicators are either positioned between the valve handles and the valve bodies or are positioned off axis from the valve handles which frustrates ease of reading especially in poorly lighted conditions or in adverse weather environments such as heavy winds, rain or snow.